October 29, 1920] 



SCIENCE 



415 



sharply as eoneentration increases until only an 

 insignificant fraction of the reactive material is 

 indicated by a measurement of the color values of 

 the solutions containing any considerable amount 

 of the reactive substance. (7) Because of the 

 peculiar form of the color curves in relation to 

 concentration, it becomes necessary for one to 

 know the approximate concentration of reactive 

 material in advance of the colorimetrie determina- 

 tion so that the colors may be developed and read 

 at such a concentration that the maximum color 

 values wOl be developed. (8) Because of the fact 

 that solutions of tyrosine and tryptophane do not 

 give the same color values at equivalent concen- 

 trations, it is impossible to measure accurately the 

 sum of these amino acids in a mixture which con- 

 tains no other reactive substances. (9) Protein 

 hydrolysates must not be boneblaeked if they are 

 to be used subsequently for a quantitative determi- 

 nation of amino acid content, for the boneblaek 

 adsorbs at least tyrosine, tryptophane and trypto- 

 phane decomposition products in appreciable 

 amounts. Whether or not other amino acids were 

 adsorbed was not determined. (10) Boneblaek 

 contains some easily oxidizable material, probably 

 reduced iron; which dissolves in acid solutions. 

 These acid solutions give the blue color with the 

 phenol reagent. 



The humin formed iy fhe acid hydrolysis of pro- 

 teins. VI. The effect of acid hydrolysis upon 

 tryptophane: George E. Holm and Boss Aiken 

 GoKTNER. Tryptophane was boiled with 20 per 

 cent, hydrochloric acid for various lengths of time 

 up to 144 hours and the solutions studied with re- 

 spect to deaminization, humin formation and ni- 

 trogen distribution. The following conclusions 

 were drawn: (1) Tryptophane is slowly altered 

 and parts of the molecule are broken down by long 

 acid hydrolysis. (2) Tryptophane, in the absence 

 of aldehydes or other reactive compounds, con- 

 tributes but an insignificant fraction of its nitrogen 

 to the "acid insoluble" humin. A much larger 

 amount of the tryptophane appears in the ' ' sol- 

 uble humin" after 144 hours' boiling with acid. 

 Since, however, a normal protein hydrolysis rarely 

 requires more than 24 hours' boiling, it appears 

 extremely improbable that the "total" humin of 

 such a hydrolysate is derived from tryptophane 

 without the intervention of some other reactive 

 compound, which we have postulated in our earlier 

 papers to be of the nature of an aldehyde. (3) 

 Tryptophane is relatively easily deaminized by 

 boiling with 20 per cent, hydrochloric acid. 



probably some of the ammonia of a normal pro- 

 tein hydrolysate is derived from tryptophane in- 

 stead of being entirely derived from amide group- 

 ings. (4) "When tryptophane has been boiled with 

 20 per cent, hydrochloric acid the distribution of 

 the nitrogen is such that errors may be introduced 

 into both the "basic" nitrogen and the "non- 

 basic nitrogen" fraction of a Van Slyke determi- 

 nation. 



The alkali reserve in pellagra: M. X. Sulli- 

 van and R.-E. Stanton. Of fifty-six separate 

 cases tested by alkali reserve by the alveolar air 

 method and by the determination of the carbon 

 dixide bound by the blood plasma, none showed a 

 marked depletion of the alkali reserve, about one 

 third showed a slightly subnormal level, while the 

 greater number of cases were within normal lim- 

 its. There is little acidosis in pellagra. 



The mosaic disease of spinach as characterized 

 by its nitrogen constituents: S. L. Jodidi, S. C. 

 MoDLTON, K. S. Maekley. Spinach plants, espe- 

 cially their tops, affected with mosaic disease, have 

 a smaller percentage of total, nitrate, acid amide, 

 mono and diamono nitrogen, but a somewhat larger 

 percentage of ammonia than normal plants, nitrous 

 acid being present in diseased plants only. This 

 is due to the fact that denitrification takes place 

 whereby nitrates are reduced to nitrites which re- 

 acting on the various nitrogenous compounds pres- 

 ent in the spinach bring about elimination of 

 nitrogen in a free state, involving also a loss of 

 nitrogen in the form of ammonia. Very little 

 denitrification, if any, takes place in the roots of 

 diseased spinach. This is evident from the fact 

 that the differences in total, nitrate, amino nitrogen 

 content, etc., of the roots of healthy and diseased 

 plants are usually quite small, running sometimes 

 in opposite direction. Conditions with regard to 

 peptide and protein nitrogen are apparently some- 

 what more complicated. In the samples examined 

 the proportion of peptide nitrogen is higher in 

 diseased tops than in normal, while the proportion 

 of protein nitrogen is higher in diseased roots than 

 in normal, this being also true of diseased leaves 

 when related to the total nitrogen. This is con- 

 ceivable since the latter is here smaller due to loss 

 through denitrification. In round figures the 

 spinach nitrogen is made up of 55 per cent, pro- 

 tein nitrogen, 4.5 per cent, diamine nitrogen, 5.5 

 per cent, monoamine nitrogen, and 6 per cent, pep- 

 tide nitrogen. This means that over 70 per cent, 

 of .the nitrogenous compounds occurring in spinach 

 have direct nutritive value. 



